1. Field of the Invention
The present invention relates to an apparatus for converting image format and methods thereof in a video signal processing system, and more particularly, to an image format converting apparatus and methods thereof by which a converted image of first-rate quality is realized when horizontal and vertical dimensions of an image are converted at any rate and at the same time, and the amount of hardware and computation necessary for an image conversion can be reduced.
2. Description of the Related Art
Generally, the term xe2x80x9cmultimediaxe2x80x9d refers to a system which can transmit information relating to characters, pictures, audio and the like and is applied to televisions, computers, videophones, and the like.
It is necessary to convert the format of a video signal during interface processing in multimedia applications in which systems of different types are combined together into a system. Such combinations could include a personal computer connected to another personal computer, a personal computer connected to a television, a television connected to a television, etc.
An example of such image format conversion is conversion of an image from 500xc3x97400 resolution to 300xc3x97300 resolution; in this case, the horizontal scale-down ratio is 5 to 3 and the vertical scale-down ration is 4 to 3.
This is basically achieved by converting such time factors as horizontal and vertical frequency, pixel frequency and the like and such dimensional factors as the horizontal and vertical size of an image.
Then the time factor-conversion is realized by using a memory buffer and the dimensional factor-conversion is realized by using filters.
For example, when five image samples are input in order to scale down an image in the ratio of 5 to 3, three image samples have to be produced.
According to the conventional format-converting method, the number of samples is interpolated by 3 to be increased by a factor of three, and then is decimated by 5 to be decreased by a factor of ⅕.
Using this process, interpolations and decimations each have to be carried out more than 30 times.
Meanwhile, according to the conventional image format-conversion method using hardware, lines (verticality) or pixels (horizontality) are skipped at predetermined intervals to scale down the image in size, and lines (verticality) or pixels (horizontality) are folded at predetermined intervals to scale up the image in size.
Such conventional methods allow the hardware to be easily realized, but there is a problem in that the image appears coarse, and in particular, characters appear broken in the case where a PC image containing many characters is scaled-down.
Conventional methods require a filter having a number of taps to prevent the quality of an image from deteriorating when converting image format; nxe2x88x921 line memory units are needed when a filter having n taps is used for scaling in a vertical direction.
Accordingly, there is a disadvantage with the conventional method thus performed because it is expensive to manufacture hardware capable of providing a high quality image when performing an image format conversion.
Accordingly, the present invention is provided to solve the aforementioned problem and it is an object of the present invention to provide an apparatus for converting an image format and methods thereof in video-signal processing systems in which a space-position in one cycle is computed in advance by using periodicity of input sequence and output sequence and the outcome resulting from the computation is repeatedly applied, so that a converted image of good quality is obtained, and at the same time, an amount of computation and size of the hardware can be reduced.
In accordance with the object of the present invention, there is provided an apparatus, comprising: an analog-to-digital converting unit for sampling original color signals at predetermined intervals and converting the sampled signals into digital signals; a color-space converting unit for converting a digital signal of the analog-to-digital converting unit into a brightness signal and a color tone signal and for outputting it; a storage unit for storing a look-up table representing linear interpolation coefficients converted in response to a conversion of an image size; a horizontal scaling unit for linearly interpolating one cycle of the brightness signal and color tone signal in response to a conversion of image size with reference to the look-up table of the storage unit, and for horizontally scaling by repeatedly outputting the outcome linearly-interpolated; a line memory unit for momentarily storing a horizontally scaled signal by the horizontal scaling unit; a vertical scaling unit for interpolating a cycle of a horizontal scaling signal provided by the line memory unit in response to the conversion of the image size with reference to the look-up table, thereby vertically scaling by repeatedly outputting the linearly interpolated data; and a frame memory unit for storing signals vertically and horizontally-scaled by the vertical scaling unit and for converting vertical and horizontal frequencies of the vertical and horizontal scaled signals.
In accordance with the object of the present invention, there is provided a method comprising the steps of: sampling each of original color signals at predetermined intervals and converting the sampled signals into digital signals; converting the digital signals transformed by the analog-to-digital converting unit into a brightness signal and a color tone signal; linearly-interpolating one cycle of the brightness and color tone signals in response to conversion of an image size with reference to a look-up table provided with linear-interpolated coefficients and horizontally-scaling by using repeatedly the linearly-interpolated data; vertically scaling the horizontally scaled signals with reference to the look-up table; and storing the vertically and horizontally scaled signals in a frame memory unit and converting vertical and horizontal frequencies of the vertically and horizontally scaled signals.